The present invention generally relates to semiconductor processing, and in particular to a system for optimal development of a photoresist material layer on a wafer.
In the semiconductor industry, there is a continuing trend toward higher device densities. To achieve these high densities there has been and continues to be efforts toward scaling down device dimensions (e.g., at submicron levels) on semiconductor wafers. In order to accomplish such high device packing density, smaller and smaller features sizes are required. This may include the width and spacing of interconnecting lines, spacing and diameter of contact holes, and the surface geometry such as corners and edges of various features.
The requirement of small features with close spacing between adjacent features requires high resolution photolithographic processes. In general, lithography refers to processes for pattern transfer between various media. It is a technique used for integrated circuit fabrication in which a silicon structure or wafer is coated uniformly with a radiation-sensitive film, the resist, and an exposing source (such as optical light, x-rays, or an electron beam) illuminates selected areas of the surface through an intervening master template, the mask, for a particular pattern. The lithographic coating or resist is generally a radiation-sensitive coating suitable for receiving a projected image of the subject pattern.
The resist can be classified into a positive type resist or a negative type resist based on the type of reaction, and a two component or a three component type based on the number of components in the resist. A positive type resist becomes more soluble in an aqueous based developer when exposed to radiation and negative type resist becomes less soluble in an aqueous based developer when exposed to radiation. A two component type includes a base resin, such as a photosensistive organic compound and a photoacid generator. A photoacid generator is a compound that is neutral, but which decomposes to form an acid upon exposure to light energy at particular wavelengths or frequencies. The photosensitive organic compound is a compound that absorbs light at different wavelengths and thereafter transfers energy to the photoacid generator to form the acid. A three component type includes a base resin, a photoacid generator and an acid-crosslinking agent. Exposure of the resist through a photomask causes the image area to become either more or less soluble (depending on the coating) in a particular solvent developer. The solvent is a base and the more soluble areas of the resist are removed in the developing process to leave the pattern image in the coating. The patterned image is used as a mask for etching the pattern into the wafer. The resist is then stripped from the wafer leaving the patterned image etched into the wafer.
Application of the resist onto the wafer is typically accomplished by using a spin coater. The spin coater is essentially a vacuum chuck rotated by a motor. The wafer is vacuum held onto the spin chuck. Typically, a nozzle supplies a predetermined amount of resist to a center area of the wafer. The wafer is then accelerated to and rotated at a certain speed, and centrifugal forces exerted on the resist cause the resist to disperse over the whole surface of the wafer. After the resist is spin coated and selectively irradiated to define a predetermined pattern, the irradiated or nonirradiated portions are removed by applying a developer. The developer is also spin coated onto the wafer by applying developer across the resist and then spin coating the developer until centrifugal forces disperse the developer over the coating of resist. After a predetermined time, the photoresist material layer becomes developed and the irradiated or nonirradiated portions are removed by rinsing or washing with a washing solution material.
However, the rate of development may vary based on the amount and concentration of the photoacid generator in the resist, the identity of the photoacid generated, the identity of the developer, the concentration and volume of the developer and the amount of time that the resist is exposed to the developer. Failure to use the appropriate amount/concentration of developer and/or appropriate exposure time for a given photoacid generator and developer results in nonuniform quality of the imaged pattern across the resist and ultimately wafer defects.
In view of the above, a system/method is needed, for dispensing an optimal volume and concentration of developer across a photoresist material layer formed on a wafer for an optimal period of development time.
The present invention provides for a system and method that facilitates the uniform development of a pattern on a photoresist material layer using a developer. The present invention accomplishes this end by considering the acid-base relationship of the photoresist material and developer and monitoring the development of water formed in the development process. Typically, photoresist material is purchased or manufactured with known concentrations of resin and photoacid generator. Therefore, by monitoring the development of acid or formation of water in the development process, the present invention can measure the acid consumption in the development process. The present invention can then utilize this information in optimizing the developer volume, developer concentration and development time to improve the quality of the developed image pattern on the photoresist material layer.
A developer plate can be employed forming a parallel plate pair with the wafer during application of the developer. The developer plate is disposed in very close proximity with respect to the wafer, such that the developer is squeezed between the two plates thereby spreading evenly the developer over the wafer. Since the developer film is stagnant, the transport of acid into base can be monitored and therefore, the development process can be monitored. Furthermore, the proximity of the developer plate to the wafer during application and the size of a plurality of apertures in the developer plate provides for improved localization with respect to development of the photoresist material layer.
In one aspect of the invention, a monitoring or measurement system is provided that measures the amount of water formed in a development process of a photoresist material. The measuring can be accomplished utilizing various techniques. For example, the measuring may be conducted on a test or reference wafer off-line utilizing conventional lab measuring techniques. Using the measured results, adjustments can be made to the developer volume, developer concentration and/or development time until an optimal result is achieved. The measuring may be accomplished by employing in situ laser scattering or laser doppler anemometry techniques. Additionally, the measuring may be accomplished by employing light scattering techniques, such as interferometry and spectrometry. The laser scattering and light scattering techniques can be employed in providing a close loop system, such as a control system for continuously improving the acid consumption of the development process.
One particular aspect of the invention relates to a method of developing a selectively irradiated photoresist material layer disposed on a semiconductor wafer. The method includes contacting the photoresist material layer with a volume of developer having a concentration for a period of time whereby the developer and an acid in the photoresist material layer interact to generate an amount of water, measuring the amount of water, determining an amount of acid consumption based on the amount of water measured and adjusting at least one of the developer volume, concentration and contact time based on the amount of acid consumption determined.
Another aspect of the invention relates to a system for monitoring development of a selectively irradiated photoresist material layer. The system includes at least one light source disposed near the selectively irradiated photoresist material layer where the at least one light source is adapted to transmit a ray of light across the selectively irradiated photoresist material layer. The system also includes at least one detector disposed near the selectively irradiated photoresist material layer where the at least one detector is adapted to receive a reflected ray of light due to the at least one light source and provide a signal corresponding to the intensity of the reflected ray of light. The system further includes a measuring system operably coupled to the at least one detector where the measuring system is adapted to receive the signal corresponding to the intensity of the ray of light and convert the signal to digital data. A processor is operatively coupled to the measuring system. The processor is adapted to receive the digital data from the measuring system and analyze the digital data wherein the difference of the intensity of the ray of light from the at least one light source to when it is received by at least one detector is proportional to an amount of water generated across the selectively irradiated photoresist material layer due to an interaction of a developer and an acid in the selectively irradiated photoresist material layer.
In yet another aspect of the invention, a system of controlling development of a selectively irradiated photoresist material layer is provided. The system includes a nozzle adapted to contact the selectively irradiated photoresist material layer with a volume of developer having a concentration for a period of time, a measuring system adapted to measure an amount of water generated on the selectively irradiated photoresist material layer due to an interaction of the developer and an acid in the selectively irradiated photoresist material layer and a processor operatively coupled to the measuring system and a developer volume and concentration control system. The processor receives data from the measuring system relating to the amount of water measured and the processor uses the data to determine an amount of acid consumption of the selectively irradiated photoresist material layer. The processor is further adapted to provide adjustment information to the developer volume and concentration control system for adjusting at least one of a developer volume, a developer concentration and a developer contact time, so that a subsequent selectively irradiated photoresist material layer having a more uniform development can be achieved.
In another aspect of the invention, a system of developing a selectively irradiated photoresist material layer disposed on a semiconductor wafer is provided.
The system includes means for applying a developer to the selectively irradiated photoresist material layer, means for measuring an amount of water generated on the selectively irradiated photoresist material layer due to an interaction of the developer and an acid in the selectively irradiated photoresist material layer and means for determining an amount of acid consumption of the selectively irradiated photoresist material layer based on the amount of water measured.
To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.